Error message
Object reference not set to the instance of an object
Problem
When loading files, an error occurs when you attempt to load a file object before you load the object to which it is attached, such as when you set the load object weight to load a design file before the design document that is related to the file.
This issue occurs because the file exists in the database before the revision to which it should be attached.
Solution
Set the load object weighting to load a file object before loading the file to which it is attached. For example, you must set the load object weight so that the design document will be loaded before the design file.
You can adjust the load object weight by selecting Data Take-On > Load Definitions > Actions 
> Create Load Object Mappings > Details > Object Weighting. For more information on setting the load object weightings, see Define load object mappings.